Parse field from quote in derive macro

[dtolnay]

Something like this:

use quote::quote;
use syn::parse::Parser;
use syn::{Field, Fields, Variant};

fn f(variant: &mut Variant) {
    match &mut variant.fields {
        Fields::Named(fields) => fields
            .named
            .push(Field::parse_named.parse2(quote! { pub a: u32 }).unwrap()),
        _ => {}
    }
}